1. Field of the Invention
The invention relates to a computer system having a parallel port installed in a portable compute such as a notebook or a laptop computer. It is mainly focused on an expansion device like a port replicator and a docking station to expand the utility of the above-mentioned portable computer. If connected to the peripheral device which needs power supply, this expansion device enables the power supply to give power to the peripheral device.
2. Description of the Prior Art
The use of a power pin in a parallel port connector may not be new in the prior art. U.S. Pat. No. 5,408,669 for a Computer System For Sensing A Cable-Connected Peripheral For Supplying Power Thereto to Stewart et al. discloses a computer system including an input/output connector for connecting to an external data peripheral, where the computer includes circuitry for detecting the presence or absence of a load on a first pin and for providing power to the external data peripheral through a second pin of the I/O connector. In this manner, the external data peripheral need not include a separate power supply, but instead is sensed and powered by the computer itself through the I/O connector.
U.S. Pat. No. 5,594,672 for a Peripheral Power Saver to Hicks discloses a device that saves energy by turning on power to a peripheral device such as a printer only when a host computer sends data to its I/O port. This invention does not have the host computer power the printer. Instead, a power saver back is used power a printer or a peripheral device. This power saver back is connected to the computer, and receives information from the computer on whether or not the peripheral should be energized.
U.S. Pat. No. 5,603,040 for a Power Management Control Unit for a Computer Peripheral to Frager et al. discloses a power management control unit and system is provided for selectively controlling ac power to one or more computer peripheral devices. The power management control unit includes a power cord connected to an ac supply and an outlet pin capable of electrically receiving the peripheral device. The management control unit also includes an ac switch electrically coupled between the power cord and the outlet pin, such that the switch can modulate conduction between the power cord and outlet pin during use.
U.S. Pat. No. 5,423,004 for a Computer With Electrically Isolated Printer Port Using Shunt Transistors Controlled by a Common Charge-Robbing Node to Porter discloses a parallel port adapter which provides a special buffering circuit on the four control lines from the system to the printer. This circuit provides a low-impedance bidirectional path for communication between the CPU and the printer whenever any of the control lines are active. The circuit uses blocking diodes on all four lines, and uses pass transistors in parallel with the blocking diodes, and uses power-robbing to turn on the pass transistors whenever the port is in use.
What is needed is a simplified circuit that provides power to a peripheral device through a parallel port cable if the peripheral needs power.